1. Field of the Invention
The present invention relates to a micro-vacuum device, and more particularly to a micro-vacuum device for large power or highly integrated large capacity.
2. Description of the Related Art
Recently, the development of a micro-vacuum tube using a field emission type cold cathode using developed Si semiconductor processing technique has been actively pursued. A conventional thermal cathode vacuum tube is used in a current density up to about 50 A/cm.sup.2 and a semiconductor device is usually used in a current density 10 to 20 A/cm.sup.2 about 100 A/cm.sup.2 at most, whereas a micro-vacuum microelement using this micro-vacuum tube technique is expected for use in a current density to 1,600 A/cm.sup.2 or more.
A representative example of such a micro-vacuum tube was disclosed in Journal of Applied Physics, Vol. 47, page 5248 (1976). A conical emitter for emitting electrons by an electric field formed in this field emission type cold cathode by a rotary oblique vapor-depositing method is known.
A representative example in which its anode is formed was disclosed in Applied Physics, Vol. 59, page 164 (1990), and Si field emission type cold cathode and an anode formed by using Si anisotropic etching is known.
A main section of this micro-vacuum tube has a structure as shown in FIG. 1. Above an Si substrate 1, a quadrangular pyramidal emitter 2 formed by Si anisotropic etching for emitting electrons is formed, and an insulating layer 3, a gate electrode layer 4, an insulating layer 5 and an anode 6 are sequentially laminated to be formed on a periphery of the emitter 2. They are contained in a vacuum vessel 7. The gate electrode layer 4 controls emission of electrons of the emitter 2. The electrons emitted from the emitter 3 are received by an anode 6.
Heretofore, a cold cathode using the abovedescribed emitter and gate electrodes has been applied to a limited example such as, for example, a display unit.
The conventional micro-vacuum tube obtains a large current density of 1,000 A/cm.sup.2 or more, though a power switching element such as a GTO (Gate Turn-Off thyristor) obtains a current density of about 10-20 A/cm.sup.2 at the time of operating the power switching element such as the GTO. Then, when a micro-vacuum tube having an on voltage of 2 V in the case of a current density of about 100 to 200 A/cm.sup.2 is formed, heat loss of energy loss particularly occurs at the time of operating. Thus, heat up to 200 to 400 W/cm.sup.2 is generated.
In this case, electrons transited in vacuum dissipate energy on a metal surface of its anode to abnormally increase its temperature, resulting in fracture and damage due to heat generation and fracture due to such as sputtering. Simultaneously, the emitter and gate electrodes are heated by heat radiation of the anode, and problems such as a current concentration at the emitter at a center of the cathode, adverse influence to other electronic devices, an electronic circuit connected to or installed at the periphery of the micro-vacuum tube occur.